M e m o r a n d u m
FROM:
Michael Baker, SBW
TO:
RTF Staff
DATE:
September 18, 2012
RE:
Phase I Review and Update Recommendations: Commercial, Domestic Hot Water
(DHW) Heater Tank
This memo documents the results of PECI’s detailed review of the UES (Unit Energy Savings) measure
Commercial Domestic Hot Water (DHW) Heater Tank. This measure has been categorized by RTF staff as
Proven and therefore this memo outlines recommendations consistent with that category. This
measure covers savings from installing a new, high-efficiency storage water heater in a commercial
building. To be eligible, the Energy Factor (EF) must exceed a certain threshold that varies based on the
size of the tank. The review focused on the derivation of the measure UES values.
Summary Recommendation. The status of this measure should be changed to Out of Compliance.
The following recommendations lead to a change in status to Out of Compliance.
 Determine if the assumed 67.5 Temperature Difference between tank and ambient
temperatures represents actual operating conditions.
 Use sales weighted Average Energy Factor, instead of the straight average of all units identified
in the AHRI databases and Summit Blue Consulting study.
The following recommendations lead to a change in status to Under Review.
 Make calculations consistent for the measure case heat loss coefficient for residential type
water heaters.
 Workbook needs to be updated to use latest ProCost template which includes Measure Cost and
EUL summary worksheets.
 Calculations from several worksheets should be consolidated and clarified on the Measure Cases
worksheet.
 Worksheets calculating interactive effects that are not incorporated in the final savings values
should be deleted.
 Clearly present the Temperature Difference assumption.
2820 Northup Way, Suite 230
Bellevue, WA 98004
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
Clearly present Average Recovery Efficiency, Average Rated Power, and Hours per Year
assumptions and use in calculations as parameters instead of hard coded values.
Review the ANSI test procedure for commercial water heaters to determine if it represents
actual operating conditions.
Limitation of Review.


The source AHRI database was not reviewed.
ANSI Z21.10.3–1998 was not reviewed to determine if the test conditions are representative of
actual operation conditions.
Alterations to Workbook and Documentation.


A worksheet called “Summary” has been added to the workbook. This worksheet describes how
measures are identified, lists important constants and their sources, describes the savings
estimation algorithm and the associated baseline and efficient case parameters and their
sources for each measure and UES component.
Renamed worksheet Cost – Residential to SBC Res Data and moved adjacent to AHRI Res Data
Workbook Calculation Errors. No errors found.
Recommendations for Updates. The RTF should implement the following recommendations:
1) Workbook Structure and Formulas
a) Energy savings for residential type water heater are calculated on row 5 of worksheet AHRI Res
Data. In cell AU5, the measure standby loss is calculated using the Measure Threshold EF (AL5).
In all other cases, the measure standby loss is calculated using the Measure Average EF of all
units that surpass the Measure Threshold EF (AQ5). This should be corrected, or at least the
discrepancy should be explained. This deficiency causes the measure status to change to Under
Review.
b) Update workbook with latest ProCost template to include Measure Cost and Effective Useful
Life (EUL) summary worksheets. This deficiency causes the measure status to change to Under
Review.
c) There are two sets of calculations of the UES for residential type water heaters. One is on the
SBC Res Data worksheet. The SBC Res Data worksheet relies on data from the Summit Blue
Consulting market survey. The other set of calculations is on the AHRI Res Data worksheet, and
it relies on data from the AHRI database. The final UES values are drawn from both sets of
calculations. To avoid confusion, the SBC Res Data and AHRI Res Data worksheets should only be
used to summarize the datasets and calculate the Average Energy Factor. Then, the existing
Measure Cases worksheet should link to the selected Average Energy Factor values to calculate
the final UES values. Similarly, the calculations of final UES values should be moved from the
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AHRI Comm Data worksheet to the Measure Cases worksheet. The Measure Cases worksheet
should include comments as to why one data source was chosen over the other for the
calculation of each measure’s UES. This deficiency causes the measure status to change to
Under Review.
d) The worksheets CBSA analysis for interactions and 6th plan lighting Interactions should be
deleted from the workbook, as the interactive effects are not considered in the final UES
calculation. This deficiency causes the measure status to change to Under Review.
e) Separate the Temperature Difference parameter from the calculation of standby loss for
residential type tanks. Temperature Difference is an important parameter and it should be
clearly presented that it is assumed to be 67.5F. This deficiency causes the measure status to
change to Under Review.
f)
The Average Recovery Efficiency (0.98), Average Rated Power (4.4 kW) and Hours per Year (8760
hr) should not be hard-coded in the heat loss coefficient formulas (e.g., see cells SBC Res Data
CH21:CI27 and AHRI Res Data AT5:AU10). They should instead be entered separately in input
cells, linked to the heat loss coefficient formula, and data sources for all three inputs should be
indicated. This deficiency causes the measure status to change to Under Review.
2) Documentation
a) None.
3) Measure Definition
4) UES Savings Estimation Method
a) None.
5) Input Parameters
a) The Temperature Difference between the water inside the water heater and the environment is
based on the DOE test procedure, which assumes a 135F water temperature and a 67.5F
ambient temperature. The Temperature Difference should instead be based on field data. As an
example, DOE is advising people to set water heaters at 120F.1 If people are heeding that
advice, then the Temperature Difference may be 15% less. Given the assumed linear
relationship of temperature difference and savings, savings would also be 15% less. Such field
data may also identify significant differences between market segments (e.g. restaurants and
hospitality) that would warrant a building type measure variant. We were not able to locate a
data source for this Temperature Difference in commercial buildings. A recent PNNL study
1
http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13090
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assumed a hot water temperature of 120F in small office buildings.1 But neither the presently
assumed value nor the PNNL study’s value have been shown to be representative of the RTF
region’s building stock, as required by the RTF’s Guidelines for input parameters to calibrated
engineering procedures. This deficiency causes the measure status to change to Out of
Compliance.
b) The Summit Blue data uses to determine weighted Average Energy Factors is 4-years old, and it
supports only a straight-line average rather than a sales-weighted average. This does not meet
the standard set by the RTF for statistical representativeness or calibration to end use. This
deficiency causes the measure status to change to Out of Compliance.
c) ANSI Z21.10.3–1998 is used to determine the Standby Loss of commercial type water heaters.
The test specification was not available for review, but we believe that the test conditions, such
as tank and ambient temperatures, may not accurately represent operating conditions for
commercial water heaters. Those test conditions should be reviewed and compared against
actual operating conditions determined from field data. This deficiency causes the measure
status to change to Under Review.
Additional Considerations
1. The Temperature Difference between the water inside the water heater and the surrounding
environment is assumed to be a constant during the full year (8760 hours). This probably
somewhat overestimates heat loss, because the Temperature Difference will be lower when the
water heater is recovering.
2. The federal standard for residential water heaters will be updated in 2015 and should be
considered for setting the sunset date. Any market survey should consider the possible impact
of the new federal standard.
1
Thornton, BA, et al (2010). “Technical Support Document: 50% Energy Savings for Small Office Buildings,”
Pacific Northwest National Laboratory.
http://www.pnl.gov/main/publications/external/technical_reports/PNNL-19341.pdf
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